1. Field:
The invention is in the field of surveying instruments providing means of field measurements used in civil engineering, geology, mineral exploration, highway and building construction, reconnaissance surveying, slope staking, building construction, and preliminary layout of land utilization planning and the like.
2. State of the Art:
In the field of surveying, precision instruments are available for making land measurements. These instruments are generally complicated in their operation as well as being expensive. These instruments also require careful handling, expert operation and accurate adjustment for leveling of the instrument itself before use at each observation station. Large organizations specializing in precise field engineering can justify the expense of these precision instruments and the skilled operatives to use them properly.
Small organizations and individuals closely related to construction, engineering, land planning and the like have a need for an uncomplicated, inexpensive instrument to accomplish the same functions but without the need for the same degree of accuracy. Although several different instruments have been proposed for measuring distance, angles, elevations, etc., a really practical, inexpensive instrument having wide diversity of functions and simplicity of operation has not been developed heretofore.
The so-called "hand level" has been widely used, even though it has a low degree of accurace, is difficult to use, and performs only the single function of leveling. The hand level generally comprises a bubble tube level mounted on top of a short scope in which a prism is mounted so that the user observes a split image, one being the fluid level, the other being the target point in the distance. Readings on the target must be taken at the precise moment that the bubble is centered in the fluid level image. This instrument being hand held by the observer and utilizing a short fluid tube has inherently, a low degree of accuracy even when operated by a steady hand and skilled observer.
Improvements are available in this type of instrument allowing it to be preadjusted to view along an inclined alignment by means of the fluid level mounted above the scope on a protractor or quadrent allowing the scope to be aimed up or down at predetermined vertical angle, but the instrument must be readjusted before a level reading or different angle observation can be taken.
In U.S. Pat. No. 2,407,416 there is shown a leveling device comprising a flat weighted mirror having a horizontal datum line inscribed thereon. The mirror is mounted on a trunnion pin for pivoting movement about a horizontal axis pendulum fashion. The trunnion pin and mirror are contained in a housing and means are provided for adjusting the setting of the mirror. The housing is supported on a tripod. In use, the device is set up vertically on its tripod. The user peers through the device with one eye so that this eye is reflected in the mirror with the pupil bisected by the datum line. On sighting past the mirror over the top of the trunnion pin, the object observed in line with the top side of the trunnion pin at the same level as the trunnion pin.